Valve normally open

FIGURE 9.10 Schematic diagram of a multisyringe separation system using solenoid valves rather than a multiposition valve. Normally open and normally closed ports on the solenoid valves are marked with open and closed circles, while the common port is unmarked. System is shown with wash and eluent solutions for Sr determination using a Sr-Resin separation column. 

Thus, as can be seen in Fig. 3.8, PIC-102 represents the pressure indicator controller number 102, and PAH is a high-pressure alarm number 102. PAHv valve-102 is a normally closed valve, activated by a solenoid that receives an electrical signal, while PICV-102 is a pneumatic valve normally opened with an actuator. 

Valve normally open I Valve normally closed... 

Valve, normally open (NO) A valve that is open when there is no actuating force. 

Scope of supply On plant On control panel In control panel PC interlock Valve normally closed Valve normally open... 

Minimum-flow loop left open at normal rates, or byj>ass around control valve is open. 

Operations The QRA team will need specific data on how the system is actually operated. For example, are the bypass valves normally left open to increase throughput, what happens when the high level alarm sounds, or do operators bypass interlocks to continue production Human actions/errors are usually dominant contributors to the real-world risks, and truthful data on actual process operations are vital to credible QRA results. Expect to commit one full-time equivalent for the life of the project. 

Manual Valve - Inadvertent operation of a block valve while the plant is onstream may expose equipment to a pressure that exceeds the maximum allowable working pressure. For the purpose of design, it is considered that only one manual valve is opened or closed and control devices are in their normal design position. A PR valve is required if the block valve is not locked or car sealed in the open position and if closure of such valve can result in overpressure. 

Water flowed from the relief pipe (20 ft elevation) to tank E610. It first flowed through the jumper to the process pipe to the normally closed blow-down valve which was open (possibly inadvertently left open or failed to seat in the attempt to pressurize the tank). About 119 gallons of water flowed through this open blow-down valve, through another, normally open, isolation valve to enter tank E610, where it reacted with MIC. 

Pilot-operated valves have the advantage of allowing operations n the set point v/ith no leakage, and the set position is not affected by ba pressure. However, they will not function if the pilot fails. If the sens line fills with hydrates or solids, the valve will open at 25% over pressure trapped above the disc (usually the normal operating pre the vessel). For this reason they should be used with care in dirty vice and liquid service. They are used extensively offshore where all platform relief valves are tied into a single header because up to 5 back-pressure will not affect the valve capacity. 

AS—Air Supply BD—Blowdown BF—Blind Flange CBD—Continuous Blowdown CD—Closed Drain CH-O—Chain Operated CSO—Car Seal Open CSC—Car Seal Closed DC—Drain Connection EBD—Emerg. Blowdown Valve ESD—Emerg. Shutdown FC—Fail Closed FO—Fail Open HC—Hose Connection IBD—Intermittent Blowdown LO—Lock Open ML—Manual Loading NC—Normally Closed NO—Normally Open OD—Open Drain... 

Relief Yalve normally selected for liquid relief service such as hydraulic systems, fire and liquid pumps, marine services, liquefied gases, and other total liquid applications. The valve characteristically opens on overpressure to relieve its rated capacity, and then reseats. 

Hose reels connected to the public water supply have the advantage that their supply of water is unlimited, although the pressure may be less than that generated in a portable extinguisher. Very large hoses are difficult to handle and lengths should not normally exceed 14 meters. Water should be immediately available when the control valve is opened. 

Closed-position indicators on the valves usually satisfy a system check . These show that the valves are nominally in the closed position but do not actually prove that there is no leakage. A proving system can be met by various systems which prove the soundness of the upstream and downstream safety shut-off valves by sequential pressurization, evacuation, mechanical over-travel with limit switches and a normally open vent valve, or other means. 

Relief valves are automatic valves, used on system lines and equipment to prevent over-pressurization. Most relief valves simply open at a preset pressure and shut when the pressure returns to normal limits. They do not maintain flow or pressure at a given amount, but prevent pressure from rising above a specified level. 

Valve 29 in line 14 is a quick opening bypass valve which is normally closed. However, in case of an emergency shutdown, this valve can be instantly opened to shut off the supply of alcohol to the reaction zone and return the alcohol stream via line 31 to alcohol supply tank 11. Such a quick opening by-pass valve normally is not employed in the nitrating acid line, since in case of an emergency shutdown, nitrating acid is employed to sweep out the tubular reactor... 

Directly actuated valves weight or spring-loaded valves that open at a predetermined pressure, and which normally close after the pressure has been relieved. The system pressure provides the motive power to operate the valve. 

A column was used to strip low-volatile materials from a high-temperature heat transfer fluid. During a maintenance procedure, water was trapped between two valves. During normal operation, one valve was opened and the hot oil came in contact with the cold water. The result was almost sudden vaporization of the water, followed by considerable damage to the column. Consider liquid water at 25°C and 1 atm. How many times does the volume increase if the water is vaporized at 100°C and 1 atm ... 

Define the equipment configuration. What valves are open or closed What are the liquid levels Is this a normal operation state ... 

A special double block and bleed system, shown in Figure 12-3, is added to every feed line to a reactor. During normal operating conditions, the block valves are open and the bleed line is closed. When the feed pump is shut off, the block valves are closed and the bleed line is open. 

Change all vacuum line air-release valves to normally open style. Pipe those valves to an argon supply equipped with a low pressure regulator (with pressure gauge) set no higher than I PSIG. 

A gas chromatograph is used for the primary separation of the components in gas oil. An automatic unit feeds the chromatograph with samples and a back-flushing unit has heen added in order to remove heavy hydrocarbons, which might otherwise choke the column. TTie carrier gas (nitrogen) is controlled by three electropneumatic valves, as shown in Fig. 4.4. In the normal mode with valve A open and valves B and C closed, carrier gas flows through columns 1 and 2 to the detector. 

Vortex breeker. It is normally a good idea to include a simple vortex breaker, as shown in Fig. 8, to prevent a vortex from developing when the liquid control valve is open. A... 

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